The Mets hope one more extra day of rest will help Neil Walker return to the starting lineup. However, manager Terry Collins also acknowledged the possibility that the second baseman’s recurring back problem could threaten the rest of his season.

“There’s a lot of concern,” said Collins, who refused to divulge Walker’s exact diagnosis following tests and an exam by doctors.

Walker has been diagnosed with a condition that is more serious than just stiffness and soreness, according to a person with knowledge of the situation, though the expectation remains that he can play through it with proper management.

“It’s going to certainly be something that he’s going to have to manage as he continues to play,” Collins said. “If he gets back in the lineup, is he going to be an everyday guy? Yeah, but with days of rest mixed in . . . Will he play five or six days in a row? No.”

Walker offered only brief comments on the matter. He dressed quickly and was curt with reporters folliwng the Mets’ 7-4 win over the Marlins.

Said Walker: “There’s nothing I can really say right now. We’ll see where we’re at [Wednesday].”

Walker has played just four games since Aug. 16. Though some of that missed time stemmed from paternity leave, most of it has been as a result of back stiffness. He has endured similar issues the last few years, including earlier this season.

After slumping for nearly two months, Walker went on a tear. Since July 27, he’s hitting .440 with seven homers and 15 RBIs. That surge has propped his season average back up to .282 with 23 homers, which equals a career high.

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But despite a strong season, a major injury would be a hit for Walker, 30, who had hoped for a long-term deal this winter when he’s scheduled to be a free agent for the first time. The Mets have interest in potentially retaining Walker.

Not leaving Las Vegas

As expected, the Mets’ Triple-A affiliate will remain in Las Vegas through 2018, the club announced on Tuesday.

The arrangement has proved to be a logistical challenge and facilities continue to be an issue. But with no other openings, the partnership will continue.

“Any time your Triple-A team’s across the country, it’s tough to get players here,” Collins said. “The only thing that’s good about it is there’s enough flights out of Vegas. Yeah, they’re red-eyes but they still get them here the next day. But that situation is what it is.”

Callups

Outfielder Michael Conforto will be among the Mets’ September callups when rosters expand on Thursday. Collins said Conforto will be “in the mix” for playing time, an indication he will again be used part time.

Conforto is hitting just .218 in the big leagues. He was demoted for the second time earlier in the month to benefit from being in the lineup every day. He has adjusted well, hitting .484 with five homers and 11 RBIs since Aug. 13.